Diphosphoryl tetrafluoride has been prepared by the dehydration of difluorophosphoric acid with phosphoric anhydride. The Raman and F 19 n.m.r. spectra have been determined and are consistent with a symmetric structure F 2 P(O)—O—P(O)F 2 . The Raman spectrum is compared with that of diphosphoryl tetrachloride and partial assignments of the frequencies to normal modes of vibration are made by comparison with the spectra of POF 3 and POCl 3 .